This invention relates generally to process challenge devices, in particular to process challenge devices using process indicators such as biological indicator organisms or biological enzymes sealed in containers made from specially chosen materials, used to assess the efficacy of procedures for the inactivation of microorganisms in industries related to health care, food packaging and preparation, and other industries that use biological indicators.
There are several conventional methods to test the effectiveness of a given sterilization, disinfection, or biological inactivation process (hereafter referred to collectively as xe2x80x9cinactivation processxe2x80x9d). A first method is to inoculate a sample product with a known quantity of a specific indicator organism (the xe2x80x9cinoculatexe2x80x9d), subject the inoculated product to the appropriate process, recover the sample inoculate, and culture the inoculate in a specific growth medium to determine whether there were any surviving organisms. A second method is to use a biological indicator which is inoculated with a known quantity of a specific indicator organism, subject the biological indicator to the appropriate process, and culture the biological indicator to determine whether there are any surviving organisms. Typically, in both the first and second methods the absence of growth of the indicator organisms in the growth medium indicates a successful inactivation process. Direct inoculation of sample product is generally done during early validation of a biological inactivation process. Biological indicators are generally used to test repeat processing. A third method is to use an indicator enzyme, subject the enzyme to the appropriate process, and then test for enzyme activity. If no activity is indicated, it is presumed that living organisms would similarly be inactivated.
Currently there are three primary inactivation processes employed in the health care industry: steam, ethylene oxide gas, and ionizing radiation. Several other processes such as dry heat, hydrogen peroxide, chlorine dioxide, peracetic acid, ozone, and plasma are also in various stages of use and acceptance.
Each of these inactivation processes require unique biological indicator organisms, growth media, and procedures to confirm sterilization effectiveness. Among the problems associated with confirming biological inactivation and thus the effectiveness of process are: (a) the lack of commercial availability of appropriate carrier media for some of the newer processes; (b) the difficulty in inoculating products to be tested due to product/package configuration; (c) the cost of using actual products that must be sacrificed for the initial process qualification and the lot-to-lot verification of the process in every process test cycle; and (d) concerns regarding worker exposure to certain of the chemical sterilants, (for example, the European Standard for ethylene oxide processing requires removal of the biological samples prior to degassing the product).
Self-contained process challenge devices containing biological indicator organisms which do not require inoculation of a product are in use in health care facilities such as hospitals. The resistance of a process challenge device to a particular biological inactivation process is given as a D Value which is defined as the exposure time required under a defined set of conditions to cause a 1-logarithm or 90% reduction in the population of a particular organism. Process challenge devices currently on the market have a single unchanging D Value. In order to create the higher resistance to the inactivation process experienced by actual product being processed, due to packaging of the product, the location of a product within a load being processed, or other factors, these devices must generally be wrapped or contained within packaging or other protective material similar to that used on the products being sterilized, so that the process challenge device is exposed to the same environment as the products being processed. Alternatively, in some cases the process challenge device is buried in the most protected location within a load being sterilized. 5 Therefore, these devices cannot be used alone to validate a biological inactivation process without additional protection from the process to simulate the higher resistance of the actual products to the process.
For example, Welsh et al., 4,839,291, discloses a process challenge device that is composed of a number of elements including an outer tube and an inner tube assembled in a manner intended to create a tortuous path to impede the flow of sterilant to the biological indicator contained within the tubes, thereby creating a D Value. Typical of many prior art devices, the device of Welsh et al. is larger and more expensive to manufacture than the present invention, and its resistance to a particular sterilization process may not be easily and accurately varied merely by using slightly different materials in construction of the device. Additionally, the materials used may not be suitable for the newer inactivation processes, such as hydrogen peroxide, ozone, and plasma, because the sterilants used may destructively react with elements of the Welsh et al. process challenge device.
It would be a significant advantage to provide a process challenge device which overcomes the disadvantages of the prior art devices, and that can, in addition, be constructed with resistance tailored to a particular biological inactivation process to avoid the need for destructive testing of product, the need for additional packaging of or protective covering over the process challenge device, or the necessity of placing one or more devices within an actual load. Therefore, what is needed is: (1) a convenient, low cost device to challenge biological inactivation process effectiveness, (2) a process challenge device that may be easily constructed with variable resistance to a particular biological inactivation process by substitution of known materials having known resistances to the particular process, (3) a process challenge device which can be constructed with a resistance to a particular biological inactivation process at least as great as the resistance of the product typically processed, so that the process challenge device may be used alone to test the inactivation process, without accompanying materials or products, (4) a package system containing a biological indicator and, optionally, an integral growth medium that is specific to any given biological inactivation process, (5) a process challenge device that can be safely, conveniently, and easily recovered for subsequent culturing to confirm and assure process effectiveness.
The present invention is a process challenge device that includes a single or multi-chamber sealed pouch or the like that contains at least one process indicator such as a biological indicator organism, biological enzyme, or other indicator used to determine the efficacy of a biological inactivation process. In embodiments having a second chamber, the second chamber may contain a cell culture medium or enzyme substrate. The pouch is composed of one or more layers of a web or film material (hereafter referred to as xe2x80x9cfilm materialxe2x80x9d). Different portions of the device may be formed of different materials.
Domestic and international regulatory guidelines permit the use of biological process challenge devices that demonstrably have resistance to sterilization equal to or greater than the material or product and package combination to be subjected to the process being tested by the process challenge device. The product and package combination (hereafter xe2x80x9cproduct-package combinationxe2x80x9d) refers to the characteristics of the product itself and of any associated packaging which may exist as these characteristics relate to or effect the product-package combinations resistance to a particular inactivation process. A product-package combination including no packaging is included in this definition.
The pouch of the present invention is fabricated from a suitable single or multiple film layer or multi-layer film laminate that is chosen to offer the appropriate level of resistance to the inactivation process. The magnitude of resistance to the inactivation process is determined by knowledge of the following factors: (1) the product and packaging configuration and characteristics, (2) the biological inactivation method of choice, and (3) the appropriate laboratory studies confirming the equivalency of biological inactivation of the device to the specific product-package combination. The resistance of the film material is typically measured by gas permeation, and temperature and chemical resistance values, which are well known in the industry.
By knowing the relevant factors, and by referencing the known gas permeation, temperature and chemical resistance values of available film materials, the specific film material or materials to be used in construction of the process challenge device may be chosen. This results in a process challenge device that can be used alone to mimic the resistance to the inactivation process experienced by the product-package combination being processed, rather than requiring that the process challenge device be processed with an actual load, or with additional packaging or protections to simulate resistance of the product-package combination to the process.
Any process indicator capable of being used to measure the efficacy of the inactivation process may be used. Biological indicator organisms are typically available commercially in the form of a carrier media such as small cellulose disks or strip carriers inoculated with a known population of a known organism. However, it is comprehended that other carrier media may be used with the present invention. Such other carrier media may include metals, fiber glass, microporous polymeric compounds including polypropylene, polyethylene, and polysulfone, and ceramics. Biological enzyme indicators are also commercially available. Such enzymes are frequently provided in the form of an enzyme tablet, but they may also be provided on a carrier media.
In some embodiments, the process challenge device of the invention may include process exposure indicators. Any means for visually indicating that the device has been exposed to the inactivation process may be used, however, a paper label that is chemically treated to change color when the device has been exposed to the biological inactivation process is preferable.
The process challenge device of the invention may also contain a separate additional chamber containing a test medium. In embodiments in which the process indicator is a biological indicator organism, the test medium may be a culture medium tailored for the specific biological indicator organism. In embodiments where the process indicator is a biological enzyme, the test medium may be an enzyme substrate chosen for use with the biological enzyme. The second chamber is separated from the first chamber containing the process indicator by a separation means, such as a valve, a clip, heat seal, or a frangible separation. The separation means between the two chambers is capable of being opened, ruptured, or removed on demand after completion of the inactivation process, to allow the culture medium or enzyme substrate, as appropriate, to contact the process indicator. In embodiments using biological indicator organisms, this initiates the beginning of the culture phase, which confirms non-survivability of the organism population and thus process efficacy. In embodiments using biological enzymes, the observation of no enzyme activity indicates that any living organisms would similarly have been inactivated. The incorporation of the culture medium or enzyme substrate into the device permits a level of convenience to the user not available in prior art inventions.